Does TCP Receive Window Size header field include the bytes in segment headers?

Question

I'm working on an implementation of TCP for a class and I'm wondering what the Window Size field actually mean.

I understand that the window size is the number of bytes, but does that number of bytes apply to:

1. the payload of the TCP Segment, not including the header or to
2. the entire TCP Segment, including the header?

Thus far, I've looked on Wikipedia:

RFC 793 states that:

The window indicates an allowed number of octets that the sender may transmit before receiving further permission.

RFC 2581 states that:

receiver's advertised window (rwnd) is a receiver-side limit on the amount of outstanding data

Neither of these make it particularly clear. Anyone?

Answer 1

It applies to the payload only. The sender can always transmit ACKs, FINs, RSTs, etc., with no payload.